Standard Life, one of Scotland's biggest employers, has warned it could relocate from Edinburgh to London if the country says Yes to independence.
The pensions and savings firm which employs 5000 people north of the border, said it was working on plans that could result in parts of its multi-billion-pound operations leaving Scotland after 189 years.
Chief executive David Nish said: "We have a longstanding policy of strict political neutrality, and at no time will we advise people on how they should vote.
"However, we have a duty and a responsibility to understand the implications of independence for our four million UK customers, our shareholders, our people and other stakeholders in our business and take whatever action is necessary to protect their interests."
The news will be seen as a huge setback to Alex Salmond’s ambitions and comes after Bank of England Deputy Governor Andrew Bailey poured cold water on the Scottish First Minister’s plans to share a financial regulator with the UK.
It also recently emerged that Lloyds Banking Group has chosen England, not Scotland, as the domicile for its TSB subsidiary.
Standard Life last week benefited from a stellar performance in its fund management arm that saw assets grow 12 per cent to £244.2 billion. The group raised its final dividend 8 per cent to 10.58p.
It also published its annual report, which revealed Nish took home pay and benefits worth just over £4 million last year, against £5.56 million in 2012.